This invention relates to an improvement of pickup cartridges used for reproducing sound in a phonographic system.
Known is a moving magnet type cartridge comprising an E-shaped yoke, a detecting coil, a magnet, a cantilever, and a sound needle, among which the detecting coil is wound around a central arm of the E-shaped yoke. When the magnet is rotated around a pivot at its center, the distribution of magnetic flux in the E-shaped yoke and therefore the value of magnetic flux in the central arm thereof is varied depending on the rotating speed. The variation of the magnetic flux in the central arm is detected by the detecting coil and converted into a signal voltage.
Although the vibration system of the moving magnet type cartridge of the above mentioned construction and operation are simple, this type of cartridge has a drawback of impairing the movability when the size of the magnet is increased for the purpose of elevating its sensitivity, and losing sensitivity when the size of the magnet is decreased for the purpose of improving the movability, because the magnet which constitutes the source of magnetic flux is rotated as an armature in the cartridge. It is of course possible to increase the number of turns of the detecting coil for elevating the sensitivity, but such a procedure deteriorates its frequency characteristics.